MIMO wireless communication systems comprise multiple-antenna wireless communication devices on both ends of a communication link, e.g., at a base station (BS) and a mobile station (MS). MIMO wireless communication techniques can enhance the radio link reliability and increase the system capacity through diversity gain and multiple signal stream transmission. Beamformed MIMO schemes have demonstrated significant benefits for MIMO systems. Through proper beamforming, the channel condition of a MIMO channel matrix can be improved and so can the signal strength of all the signal streams to be transmitted from one device to the other. However, beamformed MIMO techniques generally require spatial signature information between the antennas of the two devices on the link in order to calculate the beamforming weights.
There are at least two well known methods to capture spatial signature information and calculate beamforming weights for beamformed MIMO systems. There are referred to herein as a “two-sounding” method and a “one-sounding” method. In the two-sounding method, the MS sends training signals separately from two antennas and the MS explicitly informs the BS as to which antenna is used to send the training signals during a training session. This method requires corresponding communication protocol messages to coordinate and support the transmission of the training messages.
In the one-sounding method, the MS only sends signals from one of its antennas and consequently the BS can only receive signals from that particular MS antenna. Therefore, the BS can only obtain the required information for one MS antenna, and must estimate the channel conditions for the other antenna using some mathematical modeling techniques which cannot always be reliable.
It would be desirable to employ techniques that significantly reduce system and communication protocol requirements to capture the spatial signature information and estimate the beamforming weights for a beamformed MIMO wireless communication system.